"They have the same experience with whatever the latest thing is."
This assumption is wrong. They don't have the same experience. Their direct experience (counted as the time they spent hacking with the latest thing) might be exactly the same, but this doesn't translate to the same effective experience / capability. When I was 20, it took me much longer to become productive with any new thing than it is now when I'm 30. A 20-year old with a 6-month experience with a new language would struggle a lot even with basic concepts. A 30 (or better 40) year old, who already knows 10 other languages and a ton of frameworks would pick it up in single days or weeks and became productive very fast, leaving him much more time to dig into the advanced concepts.
When I was about 18 years old, I struggled hard with a math proof related to number theory a teacher gave me. I never solved it then when I was at school and soon moved on to some other things. Recently, when on vacation I recalled that puzzle and started thinking about it just for fun. I solved it in a few minutes by just drawing with a stick on the sand. I never studied theoretical maths nor dealt with it professionally, so I had no direct experience in doing math proofs. Somehow, my capability now is much better than it was 10 years ago. I call it "indirect experience".